A Baltimore County judge declared a mistrial Wednesday in the latest malpractice case against former cardiologist Mark Midei and the former owners of St. Joseph Medical Center after jurors failed to agree on how much the plaintiff deserved in damages.

The decision came after four days of tense deliberation among jurors who listened to six weeks of proceedings in the case. Baltimore developer Glenn Weinberg alleged that he scaled back his career and lost millions of dollars after the cardiologist wrongly led him to believe that he suffered from severe coronary artery disease and placed unnecessary stents in his heart.

Jurors found last month that Midei had breached standards of medical care in the case.

As jurors debated damages, Circuit Judge Nancy Purpura vacated the verdict finding Midei liable. The move left the hospital's former owner, Catholic Health Initiatives, as the only defendant liable for damages. Jurors had decided that while Midei was not directly employed by the hospital, he had appeared to be acting on its behalf.

Attorneys in the case declined to discuss their next moves, while outside legal observers said a new jury might be called to decide how much to award Weinberg.

Weinberg had sought $50 million in damages, contending that he was forced to retire early as a partner with the Cordish Cos. The company developed the state's largest casino, Maryland Live in Hanover, while he was recovering.

"It was disappointing that they didn't reach a verdict on damages. There were people that wanted to give us all of the damages, who wanted to give us less. They just couldn't agree," said Billy Murphy, an attorney for Weinberg. "We are gratified that they all agreed that Dr. Midei was guilty of medical malpractice."

Lawyers for the hospital's former owners and Midei declined to comment Wednesday night. Midei also declined to comment by email.

The case was the latest of hundreds involving the one-time star cardiologist and his former employer, but the first in which a jury has reached a malpractice verdict.

In May, nearly 250 patients who accused Midei of performing unnecessary stent procedures settled their cases before a jury was asked to deliberate.

The Weinberg case also was the first in which Midei testified in court. He said last month on the stand that he might have saved Weinberg's life by placing three stents in his heart.

"I am proud of the fact that I fixed him," Midei said.

Midei has denied any wrongdoing since the allegations surfaced in 2009, leading to a federal investigation and financial problems at St. Joseph. The hospital eventually was sold to the University of Maryland Medical System. Under terms of the sale, Catholic Health Initiatives is responsible for any liabilities stemming from the lawsuits.

Midei, the director of the Towson hospital's cardiac catheterization lab, was forced to leave St. Joseph, and the Maryland Board of Physicians revoked his license to practice in the state in 2011.

Several jurors declined to comment Wednesday. However, the foreman, who declined to give her name, said the deliberations were contentious at times.

On Wednesday, two jurors told the judge they could not come to an agreement with their peers. One offered to stay at the courthouse through the night. Another said in a note to the judge: "I can't do this any longer," adding that the trial had caused "too much stress on my life. I just don't see any progress being made."

Greg Dolin, co-director of the Center for Medicine and Law at the University of Baltimore School of Law, said that because of the liability verdict, he believed that there would just be a retrial on the damages.

"There are still contested issues as to how much damages are sustained, who should pay," he said.

Jurors had told the judge they had struggled to reach a verdict in an earlier phase of the trial before finally deciding that both Midei and his former employer were liable.

Weinberg, like other former Midei patients suing the doctor, contended that he suffered medical complications, emotional harm and economic distress. His attorneys said other medical experts found that Weinberg did not need stents.

Midei's lawyers contended that he acted to help his patients. They said Weinberg had suffered a minor heart attack he did not know about.

Baltimore malpractice attorney Andrew Slutkin, who is not involved in the Weinberg case but has handled other lawsuits against Midei, said the finding that Midei was liable in Weinberg's case was the first time a jury has reached a verdict against the former cardiologist.

He said such cases often wind up splitting juries on the question of damages, but the original decision showed that Weinberg's case was strong.

"Clearly, the jury is willing to find Dr. Midei responsible even in the most contested case," he said.